1. Field of the Invention
This invention relates to liquid isocyanurate-modified polymeric methylene bis(phenylisocyanate) (PMDI) compositions having high two-ring methylene bis(phenylisocyanate) (MDI) content and a viscosity comparable to standard PMDI.
This invention also relates to liquid isocyanurate-modified PMDI compositions which are useful in making rigid packaging foams which are of a substantially lighter color than those prepared from standard PMDI.
2. Description of the Material Art
Narayan et al, U.S. Pat. No. 4,382,125, disclose the production of a isocyanurate-modified PMDI compositions, and a foam made therefrom. There is no teaching in Narayan et al of mixing an isocyanurate-modified PMDI composition with a two-ring methylene bis(phenylisocyanate) (MDI) composition to give a viscosity of about 150 to 2000 mPas and a two-ring MDI content of at least 60 percent.
Narayan et al, U.S. Pat. No. 4,284,730, disclose liquid carbodiimide, uretonimine and isocyanurate containing isocyanate compositions and microcellular foams made therefrom. There is no teaching in Narayan et al of the mixing of PMDI composition with a two-ring MDI to achieve a viscosity of about 150 to 2000 mPas, and a relatively high two-ring MDI content which is suitable for making packaging foams having a lighter color than was possible using the isocyanurate compositions of the prior art.
Narayan U.S. Pat. No. 4,148,980, discloses novel carboxylate catalysts for the preparation of foams characterized by isocyanurate, urethane and urethane-isocyanurate linkages. This reference is material only in that it discloses some of the trimerization catalysts which are useful in the preparation of the isocyanurate-modified PMDI materials of the present invention.
Cenker et al, U.S. Pat. No. 4,243,756, disclose a stable liquid isocyanurate-modified polyisocyanate composition which is prepared by reacting organic polyisocyanates in the presence of catalytic amounts of alkali metal or alkaline earth metal organo-hydroxyamates or the metal salt-free acid complex of these materials at temperatures of from about 25.degree. C. to about 250.degree. C. There is no showing in Cenker et al of mixing the isocyanurate-modified polyisocyanate compositions formed thereby with a two-ring MDI composition to form an isocyanurate-modified polyisocyanate mix having a relatively high two-ring MDI content and a viscosity of about 150 to 2000 mPas.